The attempt to round up values leads to cpu values fluctuating above 100% so
remove the unnecessary complexity, and avoid going through calculations if
no nanoseconds have been registered.

-ck
---
 kernel/sched/bfs.c |   24 +++++-------------------
 1 file changed, 5 insertions(+), 19 deletions(-)

Index: linux-3.7-bfs/kernel/sched/bfs.c
===================================================================
--- linux-3.7-bfs.orig/kernel/sched/bfs.c	2013-01-29 01:22:36.408780261 +1100
+++ linux-3.7-bfs/kernel/sched/bfs.c	2013-01-29 01:22:36.807775273 +1100
@@ -256,7 +256,6 @@ struct rq {
 	u64 timekeep_clock;
 	unsigned long user_pc, nice_pc, irq_pc, softirq_pc, system_pc,
 		iowait_pc, idle_pc;
-	long account_pc;
 	atomic_t nr_iowait;
 
 #ifdef CONFIG_SMP
@@ -2475,34 +2474,21 @@ static void
 update_cpu_clock(struct rq *rq, struct task_struct *p, bool tick)
 {
 	long account_ns = rq->clock - rq->timekeep_clock;
-	struct task_struct *idle = rq->idle;
+	struct task_struct *idle;
 	unsigned long account_pc;
 
 	if (unlikely(account_ns < 0))
-		account_ns = 0;
+		goto out;
 
 	account_pc = NS_TO_PC(account_ns);
+	idle = rq->idle;
 
 	if (tick) {
-		int user_tick;
-
 		/* Accurate tick timekeeping */
-		rq->account_pc += account_pc - 128;
-		if (rq->account_pc < 0) {
-			/*
-			 * Small errors in micro accounting may not make the
-			 * accounting add up to 128 each tick so we keep track
-			 * of the percentage and round it up when less than 128
-			 */
-			account_pc += -rq->account_pc;
-			rq->account_pc = 0;
-		}
 		if (steal_account_process_tick())
 			goto ts_account;
 
-		user_tick = user_mode(get_irq_regs());
-
-		if (user_tick)
+		if (user_mode(get_irq_regs()))
 			pc_user_time(rq, p, account_pc, account_ns);
 		else if (p != idle || (irq_count() != HARDIRQ_OFFSET))
 			pc_system_time(rq, p, HARDIRQ_OFFSET,
@@ -2514,7 +2500,6 @@ update_cpu_clock(struct rq *rq, struct t
 			irqtime_account_hi_si();
 	} else {
 		/* Accurate subtick timekeeping */
-		rq->account_pc += account_pc;
 		if (p == idle)
 			pc_idle_time(rq, account_pc);
 		else
@@ -2529,6 +2514,7 @@ ts_account:
 		niffy_diff(&time_diff, 1);
 		rq->rq_time_slice -= NS_TO_US(time_diff);
 	}
+out:
 	rq->rq_last_ran = rq->timekeep_clock = rq->clock;
 }